News

Ask Matt ... what those new-fangled devices do

One of four sensors the city installed as part of a new flood detection system monitors Brittain Creek. [MATT MATTESON/Hendersonville Lightning]

By Matt Matteson, Published: January 5, 2023

Q. I noticed a new antenna on the Seventh Avenue bridge over Mud Creek. What’s that for?

It’s radar, but relax, it’s not aimed at your car. The city of Hendersonville just installed a flood sensor system designed to measure stream levels. City Stormwater Administrator Michael Huffman explained how the system works. A small radar device with a camera is mounted on the bridge and aimed downward at the stream. The solar-powered device sends a signal from the bridge to a computer in the City’s Operations Center where during a heavy rainstorm the computer operator can watch the stream rise as well as get a measurement in inches. Perhaps the most important feature is that when a stream rises to a level of concern, a text message is sent to other city officials including the police chief, fire chief and public works director. Action options can range from setting out road barricades to notifying the general public of potential flooding.

   The city’s flood sensor system is not part of the National Weather Service, which periodically posts flood warnings on your television. Huffman said those broadcasts, while valuable, are not based upon real time weather conditions. “This new system gives us the ability to have more accurate forecasts,” he said. “Sometimes when it’s raining upstream but not in Hendersonville, the streams can still rise quickly and the sensor program can detect that.”

   There are actually four sensors mounted over Hendersonville streams: two on Mud Creek (Seventh Avenue and South Main Street) one on Devil’s Fork Creek (Seventh Avenue) and one on Brittain Creek in Patton Park. The flood sensor system is new and Hendersonville’s is the first in Western North Carolina. Huffman said the system just went online in November and is being fine tuned. The system, which cost $24,000, is supported with revenue generated by the city’s stormwater permit program.

   Huffman’s team also inspects stormwater detention ponds, which are designed to hold water then slowly release it after a heavy rainfall. “It’s all about volume,” said Huffman. “If the devices get filled with leaves or sediment they are not functioning as designed.” In those cases, Huffman’s team contacts the property owner.

     Hydrology is a complex science that includes rainfall rate, constrictions, geography and soil conditions. Stormwater management, however, is really pretty simple physics — get the rainfall into the streams but keep the water within its banks. Following state and federal laws, local rules were enacted about 20 years ago that affected anyone disturbing more than an acre of land. Detention devices were required to retain the first inch of rain that falls in a 24-hour period. Those devices, typically catch basins, were also engineered to filter out pollutants. One of the most visible such basins is on Highlands Square Drive between Walmart and Sam’s Club.

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